Glass flake

ABSTRACT

A glass flake of the present invention has a composition that includes, in terms of mass %, 59≦SiO 2 &lt;65, 8≦Al 2 O 3 ≦15, 47&lt;(SiO 2 —Al 2 O 3 )≦57, 1≦MgO≦5, 20≦CaO≦30, 0&lt;(Li 2 O+Na 2 O+K 2 O)&lt;2, and 0≦TiO 2 ≦5 and that is substantially free from B 2 O 3 , F, ZnO, BaO, SrO, and ZrO 2 .

TECHNICAL FIELD

The present invention relates to glass flakes that can be mixed in, forexample, resin moldings, coating materials, inks, and cosmetics.Furthermore, the present invention also relates to resin compositions,coating materials, ink compositions, and cosmetics containing the glassflakes.

BACKGROUND ART

Glass flakes allow resin moldings to have improved strength anddimensional accuracy when being dispersed, for example, in a resinmatrix. These glass flakes are mixed in coating materials as liners andare then applied to metal or concrete surfaces.

Glass flakes exhibit metallic colors when the surfaces thereof arecoated with metal. On the other hand, they exhibit interference colorsdue to interference of reflected light when the surfaces thereof arecoated with metal oxides. That is, a glass flake coated with a coatingfilm formed of metal or metal oxide also can be used as a lusterpigment.

Luster pigments produced with glass flakes as described above arecommonly used for applications such as coating materials and cosmeticswhere color tone and luster are considered to be important.

JP 63 (1988)-201041 A describes, as suitable compositions for glassflakes, compositions of C glass produced with chemical durability beingconsidered to be important, E glass developed for electronic products,and sheet glass.

JP 2001-213639 A describes glass flakes with excellent chemicaldurability. The glass flakes with excellent chemical durability containneither diboron trioxide (B₂O₃) nor fluorine (F), which are volatilecomponents, and the content of alkali metal oxides therein is 5 mass %or lower.

Glass compositions that are not flaky but fibrous with lower contents ofalkali metal oxides are disclosed in the following publications:

-   -   JP 61 (1986)-14152A: “Glass Fiber”    -   JP 2001-515448 A: “Boron-Free Glass Fibers”    -   JP 2003-500330 A: “Glass Fiber Composition”    -   JP 2004-508265 A: “Glass Fiber Forming Compositions”

Glass flakes can be produced by using an apparatus described, forexample, in JP 5 (1993)-826 A. With the apparatus described in thepublication, a molten glass base material is blown up into a balloonshape with a blow nozzle to form a hollow glass film, and this hollowglass film is crushed with a pressure roll. Thus glass flakes can beobtained.

DISCLOSURE OF INVENTION

When the production processes as described above are taken intoconsideration, glass flakes are required to have excellent meltability,a suitable temperature-viscosity property, and a lower devitrificationtemperature than a working temperature. In this case, the workingtemperature is a temperature at which glass has a viscosity of 1000dPa·sec (1000 poise). Furthermore, the devitrification temperature isthe temperature at which crystals are formed in the molten glass basematerial and start to grow. As to the temperature-viscosity property,the working temperature is preferably 1300° C. or lower because anexcessively high working temperature particularly makes it difficult toform glass flakes.

Furthermore, when a coating film made of metal or metal oxide is to beformed on the surface of a glass flake, the glass flake may be treatedat a high temperature. Moreover, glass flakes or those with a coatingfilm may be mixed in a coating material, which may be used for a bakingfinish to be treated at a high temperature, for example. Therefore glassflakes also are required to have a sufficiently high heat resistance.

However, soda-lime glass that is used commonly as a so-called sheetglass composition contains a large amount of alkali metal oxides andtherefore does not have a sufficiently high heat resistance, which hasbeen a problem.

In the C glass composition and E glass composition among thecompositions of the glass flakes described in JP 63 (1988)-201041 A,diboron trioxide (B₂O₃) and fluorine (F) are essential components to becontained to adjust the devitrification temperature and viscosity.However, since diboron trioxide (B₂O₃) and fluorine (F) tend tovolatile, there is a possibility that they disperse during melting.Moreover, there also is a possibility of causing a problem in that, forexample, they may erode the wall of a melting furnace or a regenerativefurnace to reduce the furnace life.

Furthermore, in all the examples described in JP 2001-213639 A, glassesalways contain any one component selected from zinc oxide (ZnO), bariumoxide (BaO), strontium oxide (SrO), and zirconium oxide (ZrO₂).

However, since the zinc oxide (ZnO) tends to volatile, there is apossibility that it disperses during melting. Furthermore, there is alsoa problem in that since it volatilizes, the content thereof in the glassis difficult to control.

Generally, the raw materials of barium oxide (BaO) are expensive. Someof them require to be handled with care.

The raw materials of strontium oxide (SrO) are expensive. Since they maycontain raw materials of barium oxide (BaO). Therefore some of themrequire to be handled with care.

The zirconium oxide (ZrO₂) increases the devitrification growth rate ofglass and thereby often makes it difficult to produce glass flakesstably.

From such reasons as described above, it is desirable not to use diborontrioxide (B₂O₃), fluorine (F), zinc oxide (ZnO), barium oxide (BaO),strontium oxide (SrO), and zirconium oxide (ZrO₂) in glass flakes.

Moreover, when consideration is given to the fact that the glass flakesare to be mixed in coating materials and cosmetics, they are required tohave a high chemical durability.

With these situations in mind, the present invention is intended toprovide glass flakes with a glass composition that is substantially freefrom diboron trioxide (B₂O₃), fluorine (F), zinc oxide (ZnO), bariumoxide (BaO), strontium oxide (SrO), and zirconium oxide (ZrO₂) and thathas excellent heat resistance, chemical durability, and formability.

The present inventors devoted themselves to make a series of studiesabout a glass composition that is suitable for glass flakes and that issubstantially free from diboron trioxide (B₂O₃), fluorine (F), zincoxide (ZnO), barium oxide (BaO), strontium oxide (SrO), and zirconiumoxide (ZrO₂). As a result, they found that when the composition rangesof SiO₂ and Al₂O₃, and that of (SiO₂—Al₂O₃), which represents therelationship therebetween, were controlled, the chemical durability(especially acid resistance) was improved considerably and a glasscomposition that allowed glass flakes to be formed easily could beobtained.

That is, the present invention provides a glass flake having acomposition that includes, in terms of mass %:

-   59≦SiO₂≦65,-   8≦Al₂O₃≦15,-   47≦(SiO₂— Al₂O₃)≦57,-   1≦MgO≦5,-   20≦CaO≦30,-   0<(Li₂O+Na₂O+K₂O)<2, and-   0≦TiO₂≦5,-   and that is substantially free from B₂O₃, F, ZnO, BaO, SrO, and    ZrO₂.

According to the glass flake of the present invention, since it hasexcellent heat resistance, it is prevented from being deformed whenbeing heated to a high temperature. The glass flake of the presentinvention is excellent in chemical durability, such as acid resistance,water resistance, and alkali resistance. Particularly, it has excellentacid resistance and therefore can be used as a corrosion-resistant linerin an acid environment. In the above-mentioned composition ranges, sincethe working temperature can be controlled easily at a relatively lowtemperature, it is easy to form glass flakes.

Moreover, the present invention provides a glass flake with a coatingfilm that includes the aforementioned glass flake and a coating film.The coating film is composed mainly of metal and/or metal oxide andcovers the surface of the glass flake. The glass flake with a coatingfilm can be used as a luster pigment. The term “mainly” denotes that thecontent of the component is the highest in terms of mass %.

These glass flakes or glass flakes with a coating film can be used inresin compositions, coating materials, ink compositions, and cosmeticsby being added thereto.

In the present specification, the glass flake is a flaky particle withan average thickness t of 0.1 μm to 15 μm and an aspect ratio (averageparticle size a/average thickness t) of 2 to 1000 (see FIG. 2A). In thiscase, the average particle size a is defined as the square root of thearea S of a glass flake viewed in plane (see FIG. 2B).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view for explaining an apparatus for producingglass flakes.

FIG. 2A is a schematic view of a glass flake according to the presentinvention.

FIG. 2B is a diagram for explaining the method of determining theaverage particle size.

FIG. 3 is a schematic sectional view showing a glass flake with acoating layer.

FIG. 4 is a schematic sectional view showing a resin compositioncontaining glass flakes of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[Composition of Glass Flake]

The composition of the glass flakes of the present invention isdescribed below in detail.

<SiO₂>

Silicon dioxide (SiO₂) is a main component forming the skeleton ofglass. It also adjusts the viscosity and devitrification temperatureduring glass formation and also improves the acid resistance. When theSiO₂ content is lower than 59 mass %, the devitrification temperaturebecomes excessively high and therefore it becomes difficult to formglass flakes. Furthermore, the acid resistance of glass also isdeteriorated. On the other hand, when the SiO₂ content exceeds 65 mass%, the melting point of glass becomes excessively high and therefore itbecomes difficult to melt the raw materials uniformly.

Accordingly, the lower limit of the SiO₂ content is at least 59 mass %,preferably higher than 60 mass %, and more preferably at least 61 mass%. The upper limit of the SiO₂ content is 65 mass % or lower, preferably63 mass % or lower, and more preferably 62 mass % or lower.

The range of the SiO₂ content in terms of mass % is 59≦SiO₂≦65,preferably 60<SiO₂≦65, more preferably 60<SiO₂≦63, further preferably60<SiO₂≦62, and most preferably 61≦SiO₂≦62.

<Al₂O₃>

Aluminum oxide (Al₂O₃) is a component forming the skeleton of glass. Italso adjusts the viscosity and devitrification temperature during glassformation and also improves the water resistance. On the other hand, italso deteriorates the acid resistance of glass. When the Al₂O₃ contentis lower than 8 mass %, the viscosity and devitrification temperaturecannot be adjusted sufficiently or the water resistance cannot beimproved sufficiently. On the other hand, when the Al₂O₃ content exceeds15 mass %, the melting point of glass becomes excessively high andtherefore it becomes difficult to melt the raw materials uniformly, andthe acid resistance also is deteriorated.

Accordingly, the lower limit of the Al₂O₃ content is at least 8 mass %and preferably at least 10 mass %. The upper limit of the Al₂O₃ contentis 15 mass % or lower and preferably lower than 12 mass %.

The range of the Al₂O₃ content in terms of mass % is 8≦Al₂O₃≦15,preferably 8≦Al₂O₃≦12, and more preferably 10≦Al₂O₃≦12.

≦SiO₂—Al₂O₃>

The difference (SiO₂—Al₂O₃) between a component for improving the acidresistance of glass, SiO₂, and a component for deteriorating it, Al₂O₃,is important for the acid resistance of glass. When the difference(SiO₂—Al₂O₃) is lower than 47 mass %, the glass cannot have sufficientlyhigh acid resistance. On the other hand, when the difference(SiO₂—Al₂O₃) exceeds 57 mass %, the devitrification temperature becomesexcessively high and thereby it becomes difficult to form glass flakes.

Accordingly, the lower limit of the difference (SiO₂—Al₂O₃) is at least47 mass % and preferably higher than 49 mass %. The upper limit of thedifference (SiO₂—Al₂O₃) is 57 mass % or lower, preferably 55 mass % orlower, more preferably 54 mass % or lower, and further preferably 52mass % or lower.

The range of the difference (SiO₂—Al₂O₃) in terms of mass % is47≦(SiO₂—Al₂O₃)≦57, preferably 47≦(SiO₂—Al₂O₃)≦55, more preferably49<(SiO₂—Al₂O₃)≦55, further preferably 49<(SiO₂—Al₂O₃)≦54, and mostpreferably 49<(SiO₂—Al₂O₃)≦52.

<MgO and CaO>

Magnesium oxide (MgO) and calcium oxide (CaO) adjust the viscosity anddevitrification temperature during glass formation.

When the MgO content is lower than 1 mass %, the viscosity anddevitrification temperature cannot be adjusted sufficiently. On theother hand, when it exceeds 5 mass %, the devitrification temperaturebecomes excessively high and therefore it becomes difficult to formglass flakes.

Accordingly, the lower limit of the MgO content is at least 1 mass % andpreferably at least 3 mass %. The upper limit of the MgO content is 5mass % or lower and preferably 4 mass % or lower.

The range of the MgO content in terms of mass % is 1≦MgO≦5, preferably3≦MgO≦5, and more preferably 3≦MgO≦4.

When the CaO content is lower than 20 mass %, the viscosity anddevitrification temperature cannot be adjusted sufficiently. On theother hand, when it exceeds 30 mass %, the devitrification temperaturebecomes excessively high and therefore it becomes difficult to formglass flakes.

Accordingly, the lower limit of the CaO content is at least 20 mass %and preferably at least 21 mass %. The upper limit of the CaO content is30 mass % or lower, preferably 25 mass % or lower, and more preferably24 mass % or lower.

The range of the CaO content in terms of mass % is 20≦CaO≦30, preferably20≦CaO≦25, and more preferably 21≦CaO≦24.

<Li₂O, Na₂O, and K₂O>

Alkali metal oxides (Li₂O, Na₂O, and K₂O) adjust the viscosity anddevitrification temperature during glass formation. When no alkali metaloxide is contained, the melting point of glass becomes excessively highand therefore it becomes difficult to melt the raw materials uniformly,and it becomes also difficult to form glass flakes. On the other hand,when the sum of the contents of the alkali metal oxides is 2 mass % orlarger, the glass transition temperature is low and the heat resistanceof the glass is deteriorated.

Therefore the sum of the contents of Li₂O, Na₂O, and K₂O is in the rangeof 0<(Li₂O+Na₂O+K₂O)<2 in terms of mass %.

Especially, lithium oxide (Li₂O) has an effect of lowering the meltingpoint of glass. Accordingly, when it is added, it becomes easy to meltglass raw materials uniformly. Furthermore, since it also has an effectof lowering the working temperature, it becomes easy to form glassflakes.

Accordingly, the range of the Li₂O content in terms of mass % ispreferably 0<Li₂O<2 and more preferably 0<Li₂O≦1. However, Li₂O is notan essential component. Therefore Li₂O need not necessarily becontained, as long as at least one of Na₂O and K₂O is contained.

<TiO₂>

Titanium oxide (TiO₂) improves the meltability and chemical durabilityas well as ultraviolet absorption properties of glass. Accordingly, whenglass flakes containing TiO₂ are mixed, for example, in a resin matrixor coating material, they can suitably prevent the resin matrix orcoating material from being deteriorated. However, when the TiO₂ contentexceeds 5 mass %, the devitrification temperature of glass becomesexcessively high and therefore it becomes difficult to form glassflakes.

Accordingly, the lower limit of the TiO₂ content is 0 mass % or higherand preferably higher than 0 mass %. The upper limit of the TiO₂ contentis 5 mass % or lower and preferably 2 mass % or lower.

The range of the TiO₂ content in terms of mass % is 0≦TiO₂≦5, preferably0≦TiO₂≦2, and more preferably 0<TiO₂≦2.

<Fe>

Usually, iron (Fe) contained in glass is present in the sate of F²⁺ orFe³⁺. The components Fe³⁺ and F²⁺ improve the ultraviolet absorptionproperties and heat-ray absorption properties of glass, respectively.Accordingly, although iron (Fe) is not essential, it can be used as acomponent for adjusting the optical properties of glass. Moreover, iron(Fe) may be contained inevitably due to industrial raw materials evenwhen it is not intended to be contained.

Accordingly, the upper limit of the iron (Fe) content in terms of Fe₂O₃is 5 mass % or lower, preferably 2 mass % or lower, more preferably 0.5mass % or lower, and further preferably 0.1 mass % or lower.

The range of the Fe₂O₃ content in terms of mass % is 0≦Fe₂O₃≦5,preferably 0≦Fe₂O₃≦2, further preferably 0≦Fe₂O₃≦0.5, and mostpreferably 0≦Fe₂O₃≦0.1.

<SO₃>

Sulfur trioxide (SO₃) is not an essential component but can be used as afining agent. When the raw materials of sulfate are used as glass rawmaterials, 0.5 mass % or less of sulfur trioxide may be contained insome cases.

<B₂O₃>

Substantially no diboron trioxide (B₂O₃) is allowed to be contained inthe present invention.

<F>

Substantially no fluorine (F) is allowed to be contained in the presentinvention.

<ZnO>

Substantially no zinc oxide (ZnO) is allowed to be contained in thepresent invention.

<BaO and SrO>

Substantially no strontium oxide (SrO) and barium oxide (BaO) areallowed to be contained in the present invention.

<ZrO₂>

Substantially no zirconium oxide (ZrO₂) is allowed to be contained inthe present invention.

In the present invention, the expression “substantially no substance isallowed to be contained” denotes that it is not intended to be containedexcept for the case where it is contained inevitably, for instance, dueto an industrial raw material. Specifically, it denotes a content lowerthan 0.1 mass %, preferably lower than 0.05 mass %, and more preferablylower than 0.03 mass %.

As described above, the glass composition of the glass flakes accordingto the present invention includes, as essential components, SiO₂, Al₂O₃,MgO, CaO and (Li₂O+Na₂O+K₂O), and preferably contains TiO₂. Furthermore,it can be composed of only these components. If necessary, it cancontain iron oxide (FeO and/or Fe₂O₃) or SO₃.

[Physical Properties of Glass Flakes]

The respective physical properties of the glass flakes according to thepresent invention are described below in detail.

<Temperature Property>

The temperature at which the viscosity of molten glass is 1000 dPa·sec(1000 poise) is called “working temperature” and is considered to be themost suitable temperature for forming glass flakes.

The glass flakes can be produced, for example, using a productionapparatus as shown in FIG. 1. A glass base material 11 molten in arefractory furnace vessel 12 is blown up into a balloon shape with gasfed into a blow nozzle 15 to be formed into a hollow glass film 16. Thehollow glass film 16 is crushed with pressure rolls 17 and thus glassflakes 1 are obtained. The hollow glass film 16 has an average thicknessof 0.1 μm to 15 μm. When such a thin hollow glass film 16 is to beformed, the glass temperature decreases considerably. Accordingly, theplasticity of the hollow glass film 16 is deteriorated rapidly and itbecomes difficult to be stretched. Furthermore, the deterioration inplasticity makes it difficult for the hollow glass film 16 to growuniformly and thereby variations in glass film thickness may occur.Therefore the working temperature is preferably at least 1200° C. andmore preferably at least 1220° C.

However, when the working temperature exceeds 1300° C., the apparatusfor producing glass tends to be eroded by heat and thus the apparatuslife becomes shorter. With the decrease in working temperature, the fuelcost required for melting glass raw materials can be reduced.Accordingly, the working temperature is preferably 1265° C. or lower,more preferably 1255° C. or lower, and further preferably 1250° C. orlower.

Furthermore, with an increase in temperature difference ΔT obtained bysubtracting the devitrification temperature from the workingtemperature, devitrification tends not to occur during glass formationand thus further homogeneous glass flakes can be produced with a highyield. In the case of glass with a temperature difference ΔT of at least30° C., glass flakes can be produced with a high yield, for example,using the production apparatus as shown in FIG. 1. Accordingly, thetemperature difference ΔT is preferably at least 30° C., more preferablyat least 35° C., and further preferably at least 40° C. However, thetemperature difference ΔT is preferably at most 70° C. because in thatcase, the glass composition can be adjusted easily. Further preferably,the temperature difference ΔT is at most 60° C.

The term “devitrification” denotes that crystals that have been formedand have grown in a molten glass base material cause it to be cloudy.Glass produced from such a molten glass base material may containcrystallized mass and therefore is not preferred as glass flakes.

<Glass Transition Point>

A higher glass transition point of glass flakes allows them to havehigher heat resistance and to tend not to be deformed through processingthat involves heating at a high temperature. When the glass transitionpoint is at least 600° C., there is little possibility that the glassflakes will be deformed in the step of forming a coating film composedmainly of metal and/or metal oxide on the surface of each glass flake.Furthermore, glass flakes or glass flakes with a coating film can bemixed in a coating material, which can be used suitably for a bakingfinish, for example. The glass composition ranges defined in the presentinvention make it possible to obtain glass with a glass transition pointof at least 600° C. easily. The glass transition point of the glassflakes according to the present invention is preferably at least 600°C., more preferably at least 650° C., and further preferably at least700° C.

<Chemical Durability>

The glass flakes of the present invention are excellent in chemicaldurability such as acid resistance, water resistance, and alkaliresistance. Accordingly, the glass flakes of the present invention canbe mixed suitably, for example, in resin moldings, coating materials,cosmetics, and inks.

The index of acid resistance to be used herein is a mass reduction rateΔW₁ obtained when granular glass with an average grain size of 420 μm to590 μm was immersed in a 10-mass % sulfuric acid aqueous solution with atemperature of 80° C. for 72 hours. Lower mass reduction rates ΔW₁indicate higher acid resistance. The method of measurement thereof is inaccordance with “Measuring Method for Chemical Durability of OpticalGlass (Powder Method) 06-1975” of Japan Optical Glass IndustrialStandards (JOGIS). However, a 0.01N nitric acid aqueous solution is usedin the measurement method of JOGIS, but a 10-mass % sulfuric acidaqueous solution is used in the examples described later in thisspecification. Furthermore, the temperature of the sulfuric acid aqueoussolution is set at 80° C., and the process time in the examples is 72hours instead of 60 minutes employed in the measurement method of JOGIS.

When, for example, a coating material containing glass flakes is used asa corrosion-resistant liner in an acid environment, it is desirable thatthe glass have an acid resistance of 1.50 mass % or lower in terms ofthe above-mentioned index (mass reduction rate ΔW₁). When the massreduction rate ΔW₁ is higher than that, it cannot be expected to obtainthe corrosion resistance to be provided by the corrosion-resistant linerin the acid environment. The acid resistance of the glass in terms ofthe above-mentioned index is more preferably 0.80 mass % or lower andfurther preferably 0.50 mass % or lower.

The alkali resistance can be measured by using a sodium hydroxideaqueous solution instead of the sulfuric acid aqueous solution employedfor the method of measuring the acid resistance. The index of the alkaliresistance to be used herein is a mass reduction rate ΔW₂. The lower themass reduction rate ΔW₂, the higher the alkali resistance.

When glass flakes are used in a strong alkaline environment, forinstance, in a battery separator, it is desirable that the alkaliresistance of the glass in terms of the above-mentioned index (massreduction rate ΔW₂) be 3 mass % or lower. When the mass reduction rateΔW₂ is higher than that, the components of the glass flakes elute intoan electrolyte and the function of the separator may be damaged. Thealkali resistance of the glass in terms of the above-mentioned index ispreferably 2.0 mass % or lower, more preferably 1.5 mass % or lower, andfurther preferably 1.0 mass % or lower.

[Glass Flakes with Coating Film]

With the aforementioned glass flake 1 used as a substrate, a coatingfilm 2 composed mainly of metal and/or metal oxide is formed on thesurface thereof. Thus a glass flake with a coating film 1 a can beproduced (see FIG. 3). Preferably, the coating film 2 is formedsubstantially of metal and/or metal oxide.

The coating film 2 can be formed using at least one metal selected fromthe group consisting of silver, gold, platinum, palladium, and nickel.It can be in the form of a monolayer, a mixed layer, or multiple layers.

Furthermore, the coating film 2 can be formed using at least one metaloxide selected from the group consisting of titanium oxide, aluminumoxide, iron oxide, cobalt oxide, zirconium oxide, zinc oxide, tin oxide,and silicon oxide. It can be in the form of a monolayer, a mixed layer,or multiple layers. Especially, titanium dioxide and iron oxide arepreferred. The titanium dioxide has a high refractive index andtransparency and develops excellent interference colors. The iron oxidecan develop characteristic interference colors.

Furthermore, the coating film 2 can be a layered film formed by stackinga first film composed mainly of metal and a second film composed mainlyof metal oxide. It is not necessary to form the coating film 2 on thewhole surface of the glass flake 1 that serves as a substrate. Thecoating film 2 can be formed on part of the surface of the glass flake1.

The thickness of the coating film 2 can be selected suitably accordingto the intended use. The method of forming the coating film 2 on thesurface of the glass flake 1 can be any one of generally known methods.Examples of the method that can be used include known methods such as asputtering method, a sol-gel method, a CVD method, an LPD method, and aliquid phase method in which oxides are allowed to deposit from metalsalts onto the surface thereof.

[Mixing of Glass Flakes in, for Example, Resin Compositions, CoatingMaterials, Ink Compositions, and Cosmetics]

The glass flake 1 or glass flake with a coating film 1 a is mixed as apigment or reinforcing filler, for example, in resin compositions,coating materials, ink compositions, or cosmetics by a known method.This improves the color tone and luster thereof as well as, forinstance, dimensional accuracy and strength in the resin compositions,coating materials, and ink compositions.

FIG. 4 is a schematic sectional view for explaining an example in whichglass flakes 1 were mixed in a coating material, which was then appliedto the surface of a substrate 5. The glass flakes 1 are dispersed in aresin matrix 4 of a coating film 6.

The resin composition, coating material, ink composition, or cosmetic tobe used can be selected suitably according to the intended use as longas it is generally known. Furthermore, the mixing ratio between theglass flakes and the material to be mixed also can be selected suitably.Moreover, the method of mixing the glass flakes and the materialtogether can be any method as long as it is generally known.

For instance, when the glass flakes are mixed in a coating material, athermosetting resin, thermoplastic resin, or curing agent can beselected suitably to be used for a matrix resin.

Examples of the thermosetting resin include acrylic resin, polyesterresin, epoxy resin, phenolic resin, urea resin, fluororesin,polyester-urethane curable resin, epoxy-polyester curable resin,acrylic-polyester resin, acrylic-urethane curable resin,acrylic-melamine curable resin, and polyester-melamine curable resin.

Examples of the thermoplastic resin include polyethylene resin,polypropylene resin, petroleum resin, thermoplastic polyester resin, andthermoplastic fluororesin.

Furthermore, examples of the curing agent include polyisocyanate, amine,polyamide, polybasic acid, acid anhydride, polysulfide, trifluoroborate,acid dihydrazide, and imidazole.

When the glass flakes are mixed in a resin composition, theaforementioned various thermosetting or thermoplastic resins can be usedfor the matrix resin.

Examples of the ink composition include inks for writing instruments,such as various kinds of ball-point pens and felt-tip pens, and printinginks, such as gravure ink and offset ink. Any one of them can be used asthe ink composition.

The vehicle of the ink composition has a function of dispersing apigment and fixing ink to paper. The vehicle is composed of, forexample, resins, oil, and a solvent.

Vehicles of inks for writing instruments contain, as a resin, acrylicresin, styrene-acrylic copolymer, polyvinyl alcohol, polyacrylate,acrylic-vinyl acetate copolymer, microbially produced polysaccharidesuch as xanthan gum, or water-soluble plant polysaccharide such as guargum. Furthermore, the vehicles contain, for example, water, alcohol,hydrocarbon, or ester as a solvent.

Vehicles for gravure inks contain, as a resin, gum rosin, wood rosin,toll oil rosin, lime rosin, rosin ester, maleic resin, polyamide resin,vinyl resin, cellulose nitrate, cellulose acetate, ethyl cellulose,chlorinated rubber, cyclized rubber, ethylene-vinyl acetate copolymerresin, urethane resin, polyester resin, alkyd resin, a resin mixture of,for example, gilsonite, dammar, or shellac, mixtures of the resinsdescribed above, aqueous emulsion resins or water-soluble resinsobtained by water-solubilizing the resins described above. Furthermore,the vehicles contain, for example, hydrocarbon, alcohol, ether, ester,or water as a solvent.

Vehicles for offset inks contain: as a resin, rosin-modified phenolicresin, petroleum resin, alkyd resin, or a dry-modified resin thereof,and as oil, a plant oil such as linseed oil, tung oil, or soybean oil.Furthermore, the vehicles contain, for example, n-paraffin, isoparaffin,aromatic, naphthene, alpha-olefin, or water as a solvent.

Moreover, suitably selected common additives, such as dyes, pigments,various types of surfactants, lubricants, antifoaming agents, andleveling agents, can be mixed in the above-mentioned various vehiclecomponents.

Examples of cosmetics include a wide range of cosmetics such as facialcosmetics, makeup cosmetics, and hair cosmetics. Among them, especiallyin makeup cosmetics such as foundation, face powder, eye shadow,blusher, makeup base, nail enamel, eyeliner, mascara, lipstick, andfancy powder, the glass flakes are used suitably.

The glass flakes can be subjected to a hydrophobizing treatment suitablyaccordingly to the purpose of the cosmetics. Examples of the method ofcarrying out the hydrophobizing treatment include the following fivemethods:

-   (1) a treatment method to be carried out using methyl hydrogen    polysiloxane, high viscosity silicone oil, or a silicone compound    such as a silicone resin;-   (2) a treatment method to be carried out using a surfactant such as    an anion activator or a cation activator;-   (3) a treatment method to be carried out using a polymer compound    such as nylon, polymethyl methacrylate, polyethylene, various types    of fluororesins (such as polytetrafluoroethylene resin (PTFE), a    tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), a    tetrafluoroethylene-hexafluoropropylene copolymer (FEP), a    tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene    fluoride (PVDF), and polychloro-trifluoroethylene (PCTFE)), or    polyamino acid;-   (4) a treatment method to be carried out using, for example, a    perfluoro group-containing compound, lecithin, collagen, metallic    soap, lipophilic wax, or polyhydric alcohol partial ester or whole    ester; and-   (5) a treatment method employing a combination thereof.

However, any method other than the above-mentioned methods also can beused as long as it can be used generally for the hydrophobizingtreatment of powder.

Moreover, other materials that are used usually for cosmetics can bemixed suitably in the cosmetics as required. Examples thereof includeinorganic powder, organic powder, pigments, dyes, hydrocarbon, esters,oil components, organic solvents, resins, plasticizers, ultravioletabsorbers, antioxidants, preservatives, surfactants, moisturizingagents, fragrances, water, alcohol, and thickeners.

Examples of the inorganic powder include talc, kaolin, sericite,muscovite, phlogopite, lepidolite, biotite, lithia mica, vermiculite,magnesium carbonate, calcium carbonate, diatomaceous earth, magnesiumsilicate, calcium silicate, aluminum silicate, barium sulphate, metaltungstate, silica, hydroxyapatite, zeolite, boron nitride, and ceramicpowder.

Examples of the organic powder include nylon powder, polyethylenepowder, polystyrene powder, benzoguanamine powder,polytetrafluoroethylene powder, distyrenebenzene polymer powder, epoxypowder, acrylic powder, and microcrystalline cellulose.

Pigments are classified broadly into inorganic pigments and organicpigments.

Examples of inorganic pigments, which are described by being broken downby color, include:

-   -   inorganic white pigments: titanium oxide, zinc oxide, etc.;    -   inorganic red pigments: iron oxide (red iron oxide), iron        titanate, etc.;    -   inorganic brown pigments: gamma iron oxide, etc.;    -   inorganic yellow pigments: yellow iron oxide, yellow ocher,        etc.;    -   inorganic black pigments: black iron oxide, carbon black, etc.;    -   inorganic violet pigments: mango violet, cobalt violet, etc.;    -   inorganic green pigments: cobalt titanate, etc.; and    -   inorganic blue pigments: ultramarine, indigo, etc.

Examples of pearl pigments include titanium oxide coated mica, titaniumoxide coated bismuth oxychloride, bismuth oxychloride, titanium oxidecoated talc, argentine, and colored titanium oxide coated mica.Furthermore, examples of metal powder pigments include aluminum powderand copper powder.

Examples of organic pigments include:

red color No. 201, red color No. 202, red color No. 204, red color No.205, red color No. 220, red color No. 226, red color No. 228, red colorNo. 405, orange color No. 203, orange color No. 204, yellow color No.205, yellow color No. 401, and blue color No. 404; and

organic pigments obtained by forming lakes of the following dyes withfillers such as talc, calcium carbonate, barium sulfate, zirconiumoxide, or aluminum white:

red color No. 3, red color No. 104, red color No. 106, red color No.227, red color No. 230, red color No. 401, red color No. 505, orangecolor No. 205, yellow color No. 4, yellow color No. 5, yellow color No.202, yellow color No. 203, green color No. 3, and blue color No. 1.

Furthermore, examples of dyes include natural dyes such as chlorophylland beta-carotene.

Examples of hydrocarbon include:

squalane, liquid paraffin, vaseline, microcrystalline wax, ozokerite,ceresin, myristic acid, palmitic acid, stearic acid, oleic acid,isostearic acid, cetyl alcohol, hexadecyl alcohol, oleyl alcohol,cetyl-2-ethyl hexanoate, 2-ethylhexyl palmitate, 2-octyldodecylmyristate, di-2-neopentylglycol ethyl hexanoate, tri-2-glycerol ethylhexanoate, 2-octyldodecyl oleate, isopropyl myristate, glyceroltriisostearate, glycerol tri-coconut oil fatty acid, olive oil, avocadooil, beeswax, myristyl myristate, mink oil, and lanoline;

further silicone oil, higher fatty acid, esters of oils and fats, higheralcohol, and oil components such as wax; organic solvents such asacetone, toluene, butyl acetate, and ester acetate; resins such as alkydresin and urea resin; plasticizers such as camphor and acetyl tributylcitrate; and ultraviolet absorbers, antioxidants, preservatives,surfactants, moisturizing agents, fragrances, water, alcohol, andthickeners.

The form of the cosmetics is not particularly limited. Examples thereofinclude powder, cake, pencil, stick, ointment, liquid, emulsion, andcream.

EXAMPLES

Hereinafter, the present invention is described further in detail usingexamples and comparative examples.

Examples 1 to 15 and Comparative Examples 1 to 3

Common glass raw materials such as silica were mixed together so thatthe compositions indicated in Tables 1 to 3 were obtained, and therebybatches of the respective examples and comparative examples wereprepared. These batches were heated to 1400° C. to 1600° C. with anelectric furnace to be melted. They were kept in this state for aboutfour hours to have uniform compositions. Thereafter, each molten glasswas poured onto an iron plate and was cooled slowly to normaltemperature. Thus glass samples were obtained.

Glasses thus produced were measured for thermal expansion curves using acommercial dilatometer and then glass transition points thereof weredetermined from the thermal expansion curves. Moreover, the relationshipbetween viscosity and temperature was examined by a common platinum ballpulling method and then the working temperature was determined from theresults. Further, crushed glass with a grain size of 1.0 mm to 2.8 mmwas placed in a platinum boat and then was heated for two hours in anelectric furnace with a temperature gradient (900° C. to 1400° C.). Thenthe devitrification temperature was determined from the maximumtemperature of the place in the electric furnace corresponding to theposition where a crystal appeared. The temperature in the electricfurnace has been measured beforehand and the glass placed in apredetermined position is heated at that temperature.

These measurement results are indicated in Tables 1 to 3. With respectto the glass compositions indicated in the tables, all the values areindicated in mass %. As described above, ΔT denotes the difference intemperature obtained by subtracting the devitrification temperature fromthe working temperature. As described above, ΔW₁ denotes the index ofacid resistance and is expressed by the mass reduction rate obtainedwhen granular glass with an average grain size of 420 μm to 590 μm wasimmersed in a 10-mass % sulfuric acid aqueous solution with atemperature of 80° C. for 72 hours. As described above, ΔW₂ denotes theindex of the alkali resistance and is expressed by the mass reductionrate obtained when granular glass with an average grain size of 420 μmto 590 μm was immersed in a 10-mass % sodium hydroxide aqueous solutionwith a temperature of 80° C. for 72 hours.

TABLE 1 mass % Example 1 Example 2 Example 3 Example 4 Example 5 Example6 Example 7 Example 8 Example 9 SiO₂ 61.45 61.47 61.45 61.06 61.98 61.6761.89 61.55 61.55 Al₂O₃ 11.18 11.18 11.18 11.20 11.19 10.38 11.17 11.2011.20 SiO₂ − Al₂O₃ 50.27 50.29 50.27 49.86 50.79 51.29 50.72 50.35 50.35MgO 3.17 3.19 3.03 3.14 3.04 3.27 3.15 3.21 3.21 CaO 22.80 22.96 21.7722.53 21.79 23.48 22.62 23.05 23.05 Li₂O 0.14 0.14 0.36 0.28 0.27 — —0.19 0.09 Na₂O 0.30 0.10 0.38 0.58 0.56 0.40 0.39 — 0.39 K₂O 0.45 0.450.28 0.29 0.29 0.29 0.29 0.29 — Li₂O + Na₂O + K₂O 0.89 0.69 1.02 1.151.12 0.69 0.68 0.48 0.48 TiO₂ 0.25 0.25 1.56 0.92 0.89 0.25 0.25 0.250.25 Fe₂O₃ 0.26 0.26 — — — 0.26 0.24 0.26 0.26 Glass transition point [°C.] 729 739 711 715 717 744 748 735 741 Devitrification Temp. [° C.]1207 1211 1199 1195 1205 1228 1218 1211 1220 Working Temp. [° C.] 12501248 1242 1232 1253 1248 1263 1243 1252 ΔT [° C.] 43 37 43 37 48 20 4532 32 ΔW₁ [mass %] 0.41 0.37 0.30 0.32 0.25 0.25 0.26 0.21 0.25 ΔW₂[mass %] 1.68 1.67 1.60 1.52 1.47 1.81 1.71 1.60 1.57

TABLE 2 mass % Example 10 Example 11 Example 12 Example 13 Example 14Example 15 SiO₂ 61.47 61.16 60.90 60.84 60.37 59.79 Al₂O₃ 11.18 11.1311.08 11.16 12.72 12.34 SiO₂ − Al₂O₃ 50.29 50.03 49.82 49.68 47.65 47.45MgO 3.21 3.09 3.12 3.20 3.07 3.18 CaO 23.20 22.17 22.44 22.97 22.0722.85 Li₂O — — — — — — Na₂O 0.39 0.37 0.37 0.38 0.37 0.38 K₂O 0.29 0.280.29 0.29 0.27 0.29 Li₂O + Na₂O + K₂O 0.68 0.65 0.66 0.67 0.64 0.67 TiO₂— 1.55 0.25 0.90 0.87 0.90 Fe₂O₃ 0.26 0.26 1.55 0.26 0.26 0.26 Glasstransition point [° C.] 749 749 746 743 754 747 Devitrification Temp. [°C.] 1216 1202 1213 1204 1195 1203 Working Temp. [° C.] 1253 1253 12501250 1265 1249 ΔT [° C.] 37 51 37 46 70 46 ΔW₁ [mass %] 0.25 0.30 0.280.35 0.34 0.49 ΔW₂ [mass %] 1.75 1.55 1.74 1.63 1.55 1.57

TABLE 3 Comparative Comparative Comparative mass % Example 1 Example 2Example 3 SiO₂ 72.76 59.10 58.08 Al₂O₃ 1.88 13.10 14.29 SiO₂ − Al₂O₃70.88 46.00 43.79 MgO 3.58 2.83 3.16 CaO 7.62 24.31 22.66 Li₂O — — —Na₂O 13.20 0.03 0.38 K₂O 0.95 0.23 0.29 Li₂O + Na₂O + K₂O 14.15 0.260.67 TiO₂ — 0.04 0.89 Fe₂O₃ — 0.36 0.26 Glass transition point [° C.]553 758 751 Devitrification Temp. [° C.] 1020 1202 1198 Working Temp. [°C.] 1172 1246 1247 ΔT [° C.] 152 44 49 ΔW₁ [mass %] 0.40 0.90 1.64 ΔW₂[mass %] 14.20 1.27 1.52

The glass transition points of the glasses according to Examples 1 to 15were 711° C. to 754° C. This indicates that these glasses have excellentheat resistance.

The working temperatures of these glasses were 1232° C. to 1265° C.These temperatures are suitable for producing glass flakes.

The differences ΔT (working temperature−devitrification temperature) ofthese glasses were 20° C. to 70° C. These differences do not causedevitrification in the process of producing glass flakes.

Furthermore, these glasses had mass reduction rates ΔW₁, the index ofacid resistance, of 0.21 mass % to 0.49 mass %. This indicates thatthese glass flakes have excellent acid resistance.

Moreover, these glasses had mass reduction rates ΔW₂, the index ofalkali resistance, of 1.47 mass % to 1.81 mass %. This indicates thatthese glass flakes have excellent alkali resistance.

The glass of Comparative Example 1 was made of a sheet glass composition(soda-lime composition) that had been provided conventionally. However,this glass had a glass transition point of lower than 600° C. Thus itwas proved that the heat resistance thereof was not sufficiently high.

Furthermore, the glass of Comparative Example 1 had a mass reductionrate ΔW₂ of 14.20 mass %, which was 7.85 to 9.66 times the massreduction rates ΔW₂, 1.47 mass % to 1.81 mass %, of the glassesaccording to Examples 1 to 15.

With respect to the glass of Comparative Example 2, the contents ofsilicon dioxide (SiO₂) and aluminum oxide (Al₂O₃) are within the glasscomposition range of the present invention when considered individually.However, the difference therebetween (SiO₂—Al₂O₃) was lower by about 1mass % to 3 mass % as compared to the glass composition range defined inthe present invention and by about 1.45 mass % to 5.29 mass % ascompared to the compositions of the glasses according to Examples 1 to15.

The mass reduction rate ΔW₁ of the glass according to ComparativeExample 2 was 0.90 mass %, which was 1.84 to 4.29 times the massreduction rates ΔW₁, 0.21 mass % to 0.49 mass %, of the glassesaccording to Examples 1 to 15.

With respect to the glass of Comparative Example 3, the content ofaluminum oxide (Al₂O₃) is within the glass composition range of thepresent invention, but the content of silicon dioxide (SiO₂) is out ofthe glass composition range. Moreover, the difference therebetween(SiO₂—Al₂O₃) was lower by about 3 mass % to 5 mass % as compared to theglass composition range defined in the present invention and by about3.66 mass % to 7.50 mass % as compared to the compositions of theglasses according to Examples 1 to 15.

The mass reduction rate ΔW₁ of the glass according to ComparativeExample 3 was 1.64 mass %, which was 3.35 to 7.81 times the massreduction rates ΔW₁, 0.21 mass % to 0.49 mass %, of the glassesaccording to Examples 1 to 15.

Thus it was found that the acid resistance varied according to the valueof (SiO₂—Al₂O₃) in the composition of the glass according to the presentinvention. Furthermore, it was proved that the glasses in which thecontents of SiO₂ and Al₂O₃ as well as the value of (SiO₂—Al₂O₃) arewithin the composition range of the present invention had excellent acidresistance. Therefore it was proved that the value of (SiO₂—Al₂O₃) waseffective as an index of the acid resistance of a glass composition.

Glasses having the compositions of the present invention were found tohave excellent alkali resistance.

Subsequently, with glasses of Examples 1 to 15, glass flakes and glassflakes with a coating film were produced. First, glass having eachcomposition was re-melted in an electric furnace. This was formed intopellets while being cooled. These pellets were placed in a productionapparatus as shown in FIG. 1 and thus glass flakes with an averagethickness of 1 μm were produced.

Application Examples 1 and 2

Glass flakes having the compositions of Examples 1 and 3 thus producedeach were crushed to have suitable grain sizes. Thereafter, the surfacesof the glass flakes were coated with titanium dioxide by a liquid phasemethod. This liquid phase method was one described in JP 2003-012962 A,i.e. a method of allowing titanium dioxide to deposit on the surfaces ofglass flakes from metal salt. The glass flakes with a coating film thusproduced were observed with an electron microscope and thereby it wasconfirmed that a titanium dioxide coating film had been formed on thesurface of each glass flake.

Application Examples 3 and 4

Glass flakes having the compositions of Examples 1 and 3 each werecrushed to have suitable grain sizes. Thereafter, the surfaces of theglass flakes were coated with silver by common electroless plating. Thiscommon electroless plating was one described in Comparative Example 2 ofJP 2003-012962 A. The glass flakes with a coating film thus producedwere observed with an electron microscope and thereby it was confirmedthat a silver coating film had been formed on the surface of each glassflake.

Application Examples 5 and 6

Glass flakes having the compositions of Examples 1 and 3 each werecrushed to have suitable grain sizes. Thereafter, this was mixed withpolyester resin and thereby a polyester resin composition containingglass flakes was obtained.

Application Examples 7 and 8

The glass flakes with a coating film of Application Examples 1 and 2each were mixed with epoxy acrylate and thereby a vinyl ester coatingmaterial containing glass flakes with a coating film was obtained.

Application Examples 9 and 10

The glass flakes with a coating film of Application Examples 1 and 2each were mixed with foundation, a facial cosmetic, and thereby acosmetic containing glass flakes with a coating film was obtained.

Application Examples 11 and 12

The glass flakes with a coating film of Application Examples 1 and 2each were mixed with an ink composition obtained by suitably mixing acolorant, resin, and an organic solvent. Thus an ink compositioncontaining glass flakes with a coating film was obtained.

1. A glass flake, having a composition comprising, in terms of mass %:61<SiO₂≦65, 8≦Al₂O₃<12, 49<(SiO₂—Al₂O₃)≦57, 3≦MgO≦3.5, 20≦CaO≦22.62,0<(Li₂O+Na₂O+K₂O)<2, 0≦TiO₂≦5, and Li₂<0.36, wherein a content ratio ofSiO₂, to (MgO+CaO) is no less than 2.37 and no greater than 2.83,wherein a content of each of B₂O₃, F, ZnO, BaO, SrO, and ZrO₂ in thecomposition is less than 0.1 mass %, and wherein the glass flake has anindex of acid resistance in terms of a mass reduction rate ΔW₁ of 0.80mass % or lower.
 2. The glass flake according to claim 1, wherein therange of (SiO₂—Al₂O₃) is 49<(SiO₂—Al₂O₃)<55.
 3. The glass flakeaccording to claim 1, wherein when a temperature at which glass has aviscosity of 1000 dPa·sec is defined as a working temperature, theworking temperature is 1265° C. or lower.
 4. The glass flake accordingto claim 3, wherein a temperature difference ΔT obtained by subtractingdevitrification temperature from the working temperature is at least 30°C.
 5. A surface-coated glass flake, comprising: a glass flake accordingto claim 1; and a coating film that is composed mainly of metal and/ormetal oxide and that covers a surface of the glass flake.
 6. Thesurface-coated glass flake according to claim 5, wherein the metal is atleast one selected from the group consisting of nickel, gold, silver,platinum, and palladium.
 7. The surface-coated glass flake according toclaim 5, wherein the metal oxide is at least one selected from the groupconsisting of titanium oxide, aluminum oxide, iron oxide, cobalt oxide,zirconium oxide, zinc oxide, tin oxide, and silicon oxide.
 8. A resincomposition comprising a glass flake having a composition comprising, interms of mass%: 61<SiO₂≦65, 8≦Al₂O₃<12, 49<(SiO₂—Al₂O₃)≦57, 3≦MgO≦3.5,20≦CaO≦22.62, 0<(Li₂O+Na₂O+K₂O)<2, 0≦TiO₂≦5, and Li₂<0.36, wherein acontent ratio of SiO₂ to (MgO+CaO) is no less than 2.37, wherein acontent of each of B₂O₃, F, ZnO, BaO, SrO, and ZrO₂ in the compositionis less than 0.1 mass %, and wherein the glass flake has an index ofacid resistance in terms of a mass reduction rate ΔW₁ of 0.80 mass % orlower, or a resin composition comprising the surface-coated glass flakeaccording to claim
 5. 9. A coating material comprising a glass flakehaving a composition comprising, in terms of mass%: 61<SiO₂≦65,8≦Al₂O₃<12, 49<(SiO₂—Al₂O₃)≦57, 3≦MgO≦3.5, 20≦CaO≦22.62,0<(Li₂O+Na₂O+K₂O)<2, 0≦TiO₂≦5, and Li₂<0.36, wherein a content ratio ofSiO₂ to (MgO+CaO) is no less than 2.37, wherein a content of each ofB₂O₃, F, ZnO, BaO, SrO, and ZrO₂ in the composition is less than 0.1mass %, and wherein the glass flake has an index of acid resistance interms of a mass reduction rate ΔW₁ of 0.80 mass % or lower, or a coatingmaterial comprising the surface-coated glass flake according to claim 5.10. An ink composition comprising a glass flake having a compositioncomprising, in terms of mass%: 61<SiO₂≦65, 8≦Al₂O₃<12,49<(SiO₂—Al₂O₃)≦57, 3≦MgO≦3.5, 20≦CaO≦22.62, 0<(Li₂O+Na₂O+K₂O)<2,0≦TiO₂≦5, and Li₂<0.36, wherein a content ratio of SiO, to (MgO+CaO) isno less than 2.37, wherein a content of each of B₂O₃, F, ZnO, BaO, SrO,and ZrO₂ in the composition is less than 0.1 mass %, and wherein theglass flake has an index of acid resistance in terms of a mass reductionrate ΔW₁ of 0.80 mass % or lower, or a ink composition comprising thesurface-coated glass flake according to claim
 5. 11. A cosmeticcomprising a glass flake having a composition comprising, in terms ofmass %: 61<SiO₂≦65, 8≦Al₂O₃<12, 49<(SiO₂—Al₂O₃)≦57, 3≦MgO≦3.5,20≦CaO≦22.62, 0<(Li₂O+Na₂O+K₂O)<2, 0≦TiO₂≦5, and Li₂<0.36, wherein acontent ratio of SiO₂ to (MgO+CaO) is no less than 2.37, wherein acontent of each of B₂O₃, F, ZnO, BaO, SrO, and ZrO₂ in the compositionis less than 0.1 mass %, and wherein the glass flake has an index ofacid resistance in terms of a mass reduction rate ΔW₁ of 0.80 mass % orlower, or a cosmetic comprising the surface-coated glass flake accordingto claim
 5. 12. The glass flake according to claim 1, wherein thecomposition is free from lanthanoid oxide.
 13. The glass flake accordingto claim 1, wherein the range of (Li₂O +Na₂O +K₂O) is 0.48<(Li₂O +Na₂O+K₂O)<2.
 14. The glass flake according to claim 1, wherein the range ofTiO₂ is 0.25<TiO₂<5.
 15. The glass flake according to claim 1, whereinthe mass reduction rate ΔW₁ is 0.50 mass % or lower.
 16. The glass flakeaccording to claim 1, wherein the glass flake has an index of alkaliresistance in terms of a mass reduction rate ΔW₂ of 3 mass % or lower.17. The glass flake according to claim 1, wherein the glass flake has aworking temperature no less than 1242° C.
 18. The glass flake accordingto claim 1, wherein the glass flake has a ΔT of no greater than 48° C.,where ΔT is obtained by subtracting a devitrification temperature from aworking temperature of the glass flake.